The present proposal would extend ongoing epidemiological studies or case-control design to explore relationships of reproductive capacity and altered risk of breast and ovary cancers. One investigation involves testing of competing hypotheses of the association of delayed first childbirth with increased risk of carcinogenesis. The other would assess possible relationships of steroid hormones, such as contraceptive and post-menopausal drugs, to breast and ovary cancers. Recent work by MacMahon and colleagues showed that increased risk of breast cancer in women with fewer children may be due to late age at first childbirth. Similarly, Joly et al have shown that increased risk of ovary cancer may be due to delay in first pregnancy. A differing view could be that late childbirth or late pregnancy and carcinogenesis relate to a common hormonal etiology. A special contribution of the proposed study is to determine whether increased cancer risk differs according to whether the late childbirth or pregnancy is due to lower fertility or to a voluntary delay of pregnancy. Since the hormonal pattern resulting from early pregnancy may nor be the same as that associated with basic reproductive capacity, this proposed study, with emphasis on reasons for early or late pregnancy, will assess need for specific hormonal studies of breast and ovary cancer risk. Observations to date may be insufficient to decide whether contraceptive hormones are unrelated to breast cancer risk. Wide-scale use of these drugs warrants their continued surveillance and an extension of interest to other cancer sites such as the ovary. Likewise, post-menopausal drugs require further study. Taken all together these investigations are steps toward pin-pointing more closely those women at highest risk of breast or ovary cancer.